This invention generally relates to temperature control systems. More particularly, this invention relates to a temperature control strategy that balances a user""s desired temperature comfort level with energy cost savings responsive to changes in energy pricing.
Temperature control arrangements for buildings typically include a thermostat device that allows an individual to choose a setpoint temperature so that the heating or cooling system will operate to compensate for any difference in the actual temperature and the setpoint temperature in a conventional manner. Recent advances in thermostat devices include programmable thermostats that allow an individual to select various target temperatures at different time periods during a week, for example. Based upon the individual""s knowledge regarding occupancy and use, the setpoint temperatures can be set in a manner that minimizes energy usage and, therefore, provides a cost savings during system operation.
While programmable thermostats are an advancement, they are not capable of addressing situations where energy prices may change during one or more of the preset periods during which a setpoint temperature is selected. More recently, there has been a trend among energy providers to alter energy costs throughout a day responsive to increased usage at particular times of the day or during particular temperature extremes, for example. Conventional thermostat arrangements are not able to adequately address the need to allow an individual to realize energy cost savings in the face of changing energy prices.
One proposal is shown in U.S. Pat. No. 5,926,776, which allows a thermostat to communicate with an energy provider. In that patent, the thermostat allows an individual to select different temperature setpoints to correspond to different energy cost levels. One shortcoming of such an arrangement is that the individual is unable to predict how often or by how much the energy price will change and, therefore, may not be able to adequately select different setpoint temperatures to achieve a desired system performance and comfortable temperatures. Another shortcoming of that arrangement is that it does not account for an individual""s preferences to balance between energy cost savings and maintaining a setpoint temperature.
There is a need for an improved arrangement that accommodates varying energy price levels and balances those against an individual""s stated preference for balancing the desired comfort level with energy cost savings. This invention addresses that need in a unique manner.
In general terms, this invention is a system for controlling the operation of a heating or air conditioning system, for example, that automatically adjusts the performance of the system based upon changes in energy pricing according to an individual""s stated preference for balancing energy cost savings with desired temperature levels.
In one example system designed according to this invention, a thermostat device has an input portion that allows an individual to enter information regarding a desired setpoint temperature. The input portion also allows an individual to enter information regarding the individual""s preference for balancing between maintaining energy cost savings and maintaining a desired temperature level. The thermostat device also includes a sensor portion that provides an indication of a current temperature near the thermostat device. A communication module is capable of receiving information from an outside source remote from the thermostat device. Example information includes pricing information regarding energy cost. The communication module facilitates a controller determining a current energy price from information from the outside source. The controller determines a performance index value that indicates a balance between the user-specified desire to maintain the setpoint temperature and energy cost savings. The controller automatically adjusts the system sensitivity to a difference between the current temperature and the setpoint temperature according to the performance index value.
In one example, the controller uses an optimal control solution approach to determine the performance index value, which balances the system""s performance for maintaining the setpoint temperature with the need for energy cost savings according to a user""s specified preference between those two. According to one example, the controller automatically slows down a response time of the system to temperature differences between the setpoint temperature and the current temperature within the corresponding portion of the building.
A method of this invention for controlling a temperature regulating system includes defining a performance index that indicates a desired balance between maintaining a user selected setpoint temperature and conserving energy cost. Once a current energy cost is determined, a value of the performance index can be determined. In one example, an optimal control solution is used to determine the value of the performance index. The sensitivity of the system to the difference between the setpoint temperature and the current actual temperature is adjusted according to the performance index value.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.